Increased Cuticle Permeability Caused by a New Allele of ACETYL-COA CARBOXYLASE1 Enhances CO2 Uptake

Carbon dioxide (CO 2 ) is an essential substrate for photosynthesis in plants. CO 2 is absorbed mainly through the stomata in land plants because all other aerial surfaces are covered by a waxy layer called the cuticle. The cuticle is an important barrier that protects against extreme water loss; however, this anaerobic layer limits CO 2 uptake. Simply, in the process of adapting to a terrestrial environment, plants have acquired drought tolerance in exchange for reduced CO 2 uptake efficiency. To evaluate the extent to which increased cuticle permeability enhances CO 2 uptake efficiency, we investigated the CO 2 assimilation rate, carbon content, and dry weight of the Arabidopsis ( Arabidopsis thaliana ) mutant excessive transpiration1 ( extra1 ), whose cuticle is remarkably permeable to water vapor. We isolated the mutant as a new allele of ACETYL - COA CARBOXYLASE1 , encoding a critical enzyme for fatty acid synthesis, thereby affecting cuticle wax synthesis. Under saturated water vapor conditions, the extra1 mutant demonstrated a higher CO 2 assimilation rate, carbon content, and greater dry weight than did the wild-type plant. On the other hand, the stomatal mutant slow - type anion channel - associated1 , whose stomata are continuously open, also exhibited a higher CO 2 assimilation rate than the wild-type plant; however, the increase was only half of the amount exhibited by extra1 These results indicate that the efficiency of CO 2 uptake via a permeable cuticle is greater than the efficiency via stomata and confirm that land plants suffer a greater loss of CO 2 uptake efficiency by developing a cuticle barrier.